Abstract:

Methods and apparatus for plasma processing are provided herein. In some
embodiments, a plasma processing apparatus includes a process chamber
having an interior processing volume; a first RF coil disposed proximate
the process chamber to couple RF energy into the processing volume; and a
second RF coil disposed proximate the process chamber to couple RF energy
into the processing volume, the second RF coil disposed coaxially with
respect to the first RF coil, wherein the first and second RF coils are
configured such that RF current flowing through the first RF coil is out
of phase with RF current flowing through the RF second coil.

Claims:

1. A plasma processing apparatus, comprising: a process chamber having an
interior processing volume; a first RF coil disposed proximate the
process chamber to couple RF energy into the processing volume; and a
second RF coil disposed proximate the process chamber to couple RF energy
into the processing volume, the second RF coil disposed coaxially with
respect to the first RF coil, wherein the first and second RF coils are
configured such that RF current flowing through the first RF coil is out
of phase with RF current flowing through the second RF coil.

2. The apparatus of claim 1, wherein the first RF coil is wound in a
first direction and wherein the second RF coil is wound in a second
direction opposite the first direction.

3. The apparatus of claim 1, wherein the second RF coil is coaxially
disposed about the first RF coil.

4. The apparatus of claim 1, further comprising: a phase shifter coupled
to either the first or second RF coil for shifting the phase of the RF
current flowing therethrough.

5. The apparatus of claim 4, wherein the phase shifter shifts the phase
of the RF current such that the RF current flowing through the first RF
coil is about 180 degrees out of phase with RF current flowing through
the second RF coil.

6. A plasma processing apparatus, comprising: a process chamber having an
interior processing volume; a first RF coil disposed proximate the
process chamber to couple RF energy into the processing volume and wound
in a first direction; and a second RF coil disposed proximate the process
chamber to couple RF energy into the processing volume, the second RF
coil disposed coaxially with respect to the first RF coil and wound in a
second direction opposite the first direction such that RF current flows
through the first RF coil in the first direction and through the second
RF coil in the second direction.

7. The apparatus of claim 6, wherein RF current flowing through the first
RF coil is about 180 degrees out of phase with RF current flowing through
the second RF coil.

8. The apparatus of claim 6, wherein the second RF coil is coaxially
disposed about the first RF coil.

9. The apparatus of claim 8, wherein the first RF coil further comprises
a plurality of symmetrically arranged first coil elements and wherein the
second RF coil further comprises a plurality of symmetrically arranged
second coil elements.

10. The apparatus of claim 9, wherein the number of first coil elements
is two and the number of second coil elements is four.

11. The apparatus of claim 9, wherein the number of first coil elements
is four and the number of second coil elements is four.

12. The apparatus of claim 11, further comprising: an RF feed structure
coupled to each of the first and second coil elements to provide RF power
thereto, the RF feed structure coaxially disposed with respect to each of
the first and second coil elements.

13. The apparatus of claim 12, wherein the RF feed structure further
comprises: a first RF feed coupled to each of the first coil elements;
and a second RF feed coaxially disposed about the first RF feed and
electrically insulated therefrom, the second RF feed coupled to each of
the second coil elements.

14. The apparatus of claim 13, wherein the plurality of first coil
elements is symmetrically disposed about the first RF feed and the
plurality of second coil elements is symmetrically disposed about the
second RF feed.

15. The apparatus of claim 13, wherein the second RF feed further
comprises: a conductive tube having a first end proximate the first and
second coil elements and a second end opposite the first end.

16. The apparatus of claim 15, wherein the first and second end of the
conductive tube are separated by a length such that a magnetic field
formed by flowing RF current through the first and second RF feeds has
substantially no effect on the symmetry of an electric field formed by
flowing RF current through the first and second RF coils.

17. The apparatus of claim 13, further comprising: a heater element
disposed between the first and second RF coils and a dielectric lid of
the process chamber.

18. A method of forming a plasma, comprising: providing an RF signal
through a first RF coil; providing the RF signal through a second RF coil
coaxially disposed with respect to the first RF coil such that the RF
signal flows through the second coil out of phase with respect to the
flow of the RF signal through the first coil; and forming a plasma by
coupling the RF signal provided by the first and second RF coils to a
process gas disposed in a process chamber.

19. The method of claim 18, wherein the first and second RF coils are
wound in opposite directions.

20. The method of claim 18, wherein the RF current flowing through the
first and second RF coils are about 180 degrees out of phase.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional patent
application Ser. No. 61/254,833, filed Oct. 26, 2009, which is herein
incorporated by reference in its entirety.

[0003] Inductively coupled plasma (ICP) process reactors generally form
plasmas by inducing current in a process gas disposed within the process
chamber via one or more inductive coils disposed outside of the process
chamber. The inductive coils may be disposed externally and separated
electrically from the chamber by, for example, a dielectric lid. When
radio frequency (RF) current is fed to the inductive coils via an RF feed
structure from an RF power supply, an inductively coupled plasma can be
formed inside the chamber from an electric field generated by the
inductive coils.

[0004] In some reactor designs, the reactor may be configured to have
concentric inner and outer inductive coils. The inventors have discovered
that additive electric field properties (due to destructive interference
of the magnetic fields induced by the coils) between the inner and outer
coils can result in non-uniformities in the electric field distribution
of the plasma formed at the substrate level away from the coils. For
example, due to etch rate non-uniformities caused by the non-uniform
electric field distribution in the plasma, a substrate etched by such a
plasma may result in a non-uniform etch pattern on the substrate, such as
an M-shaped etch pattern, e.g., a center low and edge low etch surface
with peaks between the center and edge. The inventor's have further
observed that adjusting the power ratio between the inner and outer coils
to control the severity of the non-uniformity is not sufficient to
completely eliminate the non-uniformity. Moreover, in order to meet the
critical dimension requirements of advanced device nodes, e.g., about 32
nm and below, the remaining etch pattern non-uniformities due to this
phenomenon may need to be further reduced or eliminated.

[0005] Accordingly, the inventors have devised a plasma process apparatus
to better control plasma processing non-uniformity.

SUMMARY

[0006] Methods and apparatus for plasma processing are provided herein. In
some embodiments, a plasma processing apparatus includes a process
chamber having an interior processing volume; a first RF coil disposed
proximate the process chamber to couple RF energy into the processing
volume; and a second RF coil disposed proximate the process chamber to
couple RF energy into the processing volume, the second RF coil disposed
coaxially with respect to the first RF coil, wherein the first and second
RF coils are configured such that RF current flowing through the first RF
coil is out of phase with RF current flowing through the second RF coil.

[0007] In some embodiments, a plasma processing apparatus includes a
process chamber having an interior processing volume; a first RF coil
disposed proximate the process chamber to couple RF energy into the
processing volume and wound in a first direction; and a second RF coil
disposed proximate the process chamber to couple RF energy into the
processing volume, the second RF coil disposed coaxially with respect to
the first RF coil and wound in a second direction opposite the first
direction such that RF current flows through the first RF coil in the
first direction and through the second RF coil in the second direction.

[0008] In some embodiments, a method of forming a plasma includes
providing an RF signal through a first RF coil; providing the RF signal
through a second RF coil coaxially disposed with respect to the first RF
coil such that the RF signal flows through the second coil out of phase
with respect to the flow of the RF signal through the first coil; and
forming a plasma by coupling the RF signal provided by the first and
second RF coils to a process gas disposed in a process chamber. Other and
further embodiments of the present invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention, briefly summarized above and
discussed in greater detail below, can be understood by reference to the
illustrative embodiments of the invention depicted in the appended
drawings. It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are therefore
not to be considered limiting of its scope, for the invention may admit
to other equally effective embodiments.

[0010] FIG. 1 depicts a schematic side view of an inductively coupled
plasma reactor in accordance with some embodiments of the present
invention.

[0011] FIG. 2 depicts a schematic top view of a pair of RF coils of an
inductively coupled plasma reactor in accordance with some embodiments of
the present invention.

[0013] FIGS. 4A-B depict an RF feed structure in accordance with some
embodiments of the present invention.

[0014] FIGS. 5A-B depict schematic top views of an inductively coupled
plasma apparatus in accordance with some embodiments of the present
invention.

[0015] FIG. 6 depicts a flow chart for a method of forming a plasma in
accordance with some embodiments of the present invention.

[0016] To facilitate understanding, identical reference numerals have been
used, where possible, to designate identical elements that are common to
the figures. The figures are not drawn to scale and may be simplified for
clarity. It is contemplated that elements and features of one embodiment
may be beneficially incorporated in other embodiments without further
recitation.

DETAILED DESCRIPTION

[0017] Methods and apparatus for plasma processing are provided herein.
The inventive methods and plasma processing apparatus advantageously
provide a more uniform plasma as compared to conventional apparatus, thus
providing a more uniform processing result on a substrate being processed
with the plasma. For example, a plasma formed utilizing the inventive
plasma apparatus has an improved electric field distribution, which
provides a more uniform plasma and can be utilized to produce a more
uniform process, such as an etch pattern on a surface of a substrate.

[0018] FIG. 1 depicts a schematic side view of an inductively coupled
plasma reactor (reactor 100) in accordance with some embodiments of the
present invention. The reactor 100 may be utilized alone or, as a
processing module of an integrated semiconductor substrate processing
system, or cluster tool, such as a CENTURA® integrated semiconductor
wafer processing system, available from Applied Materials, Inc. of Santa
Clara, Calif. Examples of suitable plasma reactors that may
advantageously benefit from modification in accordance with embodiments
of the present invention include inductively coupled plasma etch reactors
such as the DPS® line of semiconductor equipment (such as the
DPS®, DPS® II, DPS® AE, DPS® G3 poly etcher, DPS® G5,
or the like) also available from Applied Materials, Inc. The above
listing of semiconductor equipment is illustrative only, and other etch
reactors, and non-etch equipment (such as CVD reactors, or other
semiconductor processing equipment) may also be suitably modified in
accordance with the present teachings.

[0019] The reactor 100 includes an inductively coupled plasma apparatus
102 disposed atop a process chamber 104. The inductively coupled plasma
apparatus includes an RF feed structure 106 for coupling an RF power
supply 108 to a plurality of RF coils, e.g., a first RF coil 110 and a
second RF coil 112. The plurality of RF coils are coaxially disposed
proximate the process chamber 104 (for example, above the process
chamber) and are configured to inductively couple RF power into the
process chamber 104 to form a plasma from process gases provided within
the process chamber 104.

[0020] The RF power supply 108 is coupled to the RF feed structure 106 via
a match network 114. A power divider 105 may be provided to adjust the RF
power respectively delivered to the first and second RF coils 110, 112.
The power divider 105 may be coupled between the match network 114 and
the RF feed structure 106. Alternatively, the power divider may be a part
of the match network 114, in which case the match network will have two
outputs coupled to the RF feed structure 106--one corresponding to each
RF coil 110, 112. The power divider is discussed in more detail below in
accordance with the embodiments illustrated in FIG. 4.

[0021] The RF feed structure 106 couples the RF current from the power
divider 116 (or the match network 114 where the power divider is
incorporated therein) to the respective RF coils. In some embodiments,
the RF feed structure 106 may be configured to provide the RF current to
the RF coils in a symmetric manner, such that the RF current is coupled
to each coil in a geometrically symmetric configuration with respect to a
central axis of the RF coils, such as by a coaxial structure.

[0022] The reactor 100 generally includes the process chamber 104 having a
conductive body (wall) 130 and a dielectric lid 120 (that together define
a processing volume), a substrate support pedestal 116 disposed within
the processing volume, the inductively coupled plasma apparatus 102, and
a controller 140. The wall 130 is typically coupled to an electrical
ground 134. In some embodiments, the support pedestal 116 may provide a
cathode coupled through a matching network 124 to a biasing power source
122. The biasing source 122 may illustratively be a source of up to 1000
W at a frequency of approximately 13.56 MHz that is capable of producing
either continuous or pulsed power, although other frequencies and powers
may be provided as desired for particular applications. In other
embodiments, the source 122 may be a DC or pulsed DC source.

[0023] In some embodiments, a link (not shown) may be provided to couple
the RF power supply 108 and the biasing source 122 to facilitate
synchronizing the operation of one source to the other. Either RF source
may be the lead, or master, RF generator, while the other generator
follows, or is the slave. The link may further facilitate operating the
RF power supply 108 and the biasing source 122 in perfect
synchronization, or in a desired offset, or phase difference. The phase
control may be provided by circuitry disposed within either or both of
the RF source or within the link between the RF sources. This phase
control between the source and bias RF generators (e.g., 108, 122) may be
provided and controlled independent of the phase control over the RF
current flowing in the plurality of RF coils coupled to the RF power
supply 108. Further details regarding phase control between the source
and bias RF generators may be found in commonly owned, U.S. patent
application Ser. No. 12/465,319, filed May 13, 2009 by S. Banna, et al.,
and entitled, "METHOD AND APPARATUS FOR PULSED PLASMA PROCESSING USING A
TIME RESOLVED TUNING SCHEME FOR RF POWER DELIVERY," which is hereby
incorporated by reference in its entirety.

[0024] In some embodiments, the dielectric lid 120 may be substantially
flat. Other modifications of the chamber 104 may have other types of lids
such as, for example, a dome-shaped lid or other shapes. The inductively
coupled plasma apparatus 102 is typically disposed above the lid 120 and
is configured to inductively couple RF power into the process chamber
104. The inductively coupled plasma apparatus 102 includes the first and
second coils 110, 112, disposed above the dielectric lid 120. The
relative position, ratio of diameters of each coil, and/or the number of
turns in each coil can each be adjusted as desired to control, for
example, the profile or density of the plasma being formed via
controlling the inductance on each coil. Each of the first and second
coils 110, 112 is coupled through the matching network 114 via the RF
feed structure 106, to the RF power supply 108. The RF power supply 108
may illustratively be capable of producing up to 4000 W at a tunable
frequency in a range from 50 kHz to 13.56 MHz, although other frequencies
and powers may be provided as desired for particular applications.

[0025] The first and second RF coils 110, 112 can be configured such that
the phase of the RF current flowing through the first RF coil can be out
of phase with respect to the phase of the RF current flowing through the
RF second RF coil. As used herein, the term "out of phase" can be
understood to mean that the RF current flowing through the first RF coil
is flowing in an opposite direction to the RF current flowing through the
second RF coil, or that the phase of the RF current flowing through the
first RF coil is shifted with respect to the RF current flowing through
the second RF coil.

[0026] For example, in conventional apparatus, both RF coils are typically
wound in the same direction. As such, the RF current is flowing in the
same direction in both coils, either clockwise or counterclockwise. The
same direction of the winding dictates that the RF current flowing in the
two RF coils are always in phase. In the present invention, the inventors
have examined providing RF current out of phase between the two coils by
either external means or by physically winding one of the coils in the
opposite direction, thus altering the original phase. By controlling the
phase between the coils the inventors have discovered the ability to
reduce and eliminate non-uniform etch results, such as the M-shape etch
pattern, and furthermore to control the processing (such as etch rate)
pattern from center high, to edge high or to a flat and uniform
processing pattern. By providing out of phase RF current between the
coils and by controlling the current ratio between the inner and outer
coil the inventors have provided an apparatus that facilitates control
over the processing pattern to achieve improved uniformity across the
substrate.

[0027] By providing out of phase RF current between the coils, the
apparatus reverses the destructive interference between the
electromagnetic fields generated by each coil to be constructive, and,
therefore, the typical constructive electric field plasma properties
within the reactor may be similarly reversed. For example, the present
apparatus may be configured to increase the electric field proximate each
of the first and second coils and decrease the electric field between the
coils by providing out of phase RF current flowing along the first and
second coils. In some embodiments, such as where the RF current in each
of the coils is completely out of phase (e.g., reverse current flow or
180 phase difference) the electric fields may be maximized (or localized)
proximate each of the first and second coils and minimized (or null)
between the coils due to destructive interference between opposing
electric fields. The inventors have discovered that a plasma formed using
such a coil configuration can advantageously have an improved, e.g., a
more uniform, electric field distribution and that components of the
plasma may diffuse into the null region of the electric field to provide
a more uniform plasma.

[0028] In some embodiments, the direction of the RF current flowing
through each coil can be controlled by the direction in which the coils
are wound. For example, as illustrated in FIG. 2, the first RF coil 110
can be wound in a first direction 202 and the second RF coil 112 can be
wound in a second direction 204 which is opposite the first direction
202. Accordingly, although the phase of the RF signal provided by the RF
power supply 108 is unaltered, the opposing winding directions 202, 204
of the first and second RF coils 110, 112 cause the RF current to be out
of phase, e.g., to flow in opposite directions.

[0029] In some embodiments, a power divider, such as a dividing capacitor,
may be provided between the RF feed structure 106 to control the relative
quantity of RF power provided by the RF power supply 108 to the
respective first and second coils. For example, as shown in FIG. 1, a
power divider 105 may be disposed in the line coupling the RF feed
structure 106 to the RF power supply 108 for controlling the amount of RF
power provided to each coil (thereby facilitating control of plasma
characteristics in zones corresponding to the first and second coils). In
some embodiments, the power divider 105 may be incorporated into the
match network 114. In some embodiments, after the power divider 105, RF
current flows to flows to the RF feed structure 106 where it is
distributed to the first and second RF coils 110, 112. Alternatively, the
split RF current may be fed directly to each of the respective first and
second RF coils.

[0030] By adjusting the power ratio in combination with the phase of the
RF signal flowing through each of the first and second coils, the
inventors have discovered that undesired processing non-uniformities
(such as the M-shape etch profile of a substrate surface) may be
controlled. For example, FIGS. 3A-B illustratively depict graphs of etch
rate profiles generated using conventional apparatus and an embodiment of
the inventive apparatus as disclosed herein. These graphs illustratively
depict data from actual tests and observations performed by the
inventors. FIG. 3A depicts an etch rate profile graph of the etch rate
(axis 310) radially along a substrate surface (axis 312) for a plurality
of power ratios between the first and second coils in a conventional
apparatus (plots 302A, 304A and 306A). While some control over the etch
rate profile can be achieved by adjusting the power ratio in the
conventional apparatus, as shown in FIG. 3A, the inventors have
discovered that any adjustment of the power ratio still results in
inadequate overall uniformity, and in particular, poor edge profile
tenability (e.g., each power ratio provides a limited effect at the edge
of the etch profile).

[0031] In contrast, FIG. 3B depicts an etch rate profile graph of the etch
rate (axis 310) radially along a substrate surface (axis 312) for a
plurality of the same power ratios between the first and second coils in
an apparatus in accordance with embodiments of the present invention
having the RF current flowing through the first and second RF coils 180
degrees out of phase (plots 302B, 304B and 306B). Specifically, by making
the same power ratio adjustments in the inventive apparatus as shown in
FIG. 3B, the inventors have discovered that a significantly greater
degree of uniformity control can be achieved. In addition, greatly
improved edge profile tunability can be also achieved. As can be seen
from the graph in FIG. 3B, the inventive apparatus can provide a
substantially uniform etch rate profile by tuning the power ratio (e.g.,
304B) and can also provide a significantly greater edge profile
tunability as compared to a conventional apparatus. For example, by
controlling the power ratio in a chamber configured to have RF current
flowing through the two RF coils out of phase, the uniformity profile can
be controlled to provide center high and edge low etch rates,
substantially flat etch rates, or center low and edge high etch rates. As
these results are due to the plasma uniformity, such control is also
transferrable to other processes or results (such as plasma treatment,
deposition, annealing, or the like) where plasma uniformity provides
control over such processes or results.

[0032] Embodiments of an exemplary RF feed structure 106 that may be
utilized in combination with the out of phase RF coil apparatus disclosed
herein are described below and depicted in further detail in FIGS. 4A-B.
Further details regarding the exemplary RF feed structure may be found in
U.S. Patent Application Ser. No. 61/254,838, filed on Oct. 26, 2009, by
Z. Chen, et al., and entitled "RF FEED STRUCTURE FOR PLASMA PROCESSING,"
which is hereby incorporated by reference in its entirety. For example,
FIGS. 4A-B depicts the RF feed structure 106 in accordance with some
embodiments of the present invention. As depicted in FIG. 4A, the RF feed
structure 106 may include a first RF feed 402 and a second RF feed 404
coaxially disposed with respect to the first RF feed 402. The first RF
feed 402 is electrically insulated from the second RF feed 404. In some
embodiments, and as illustrated, the second RF feed 404 is coaxially
disposed about the first RF feed 402, for example, along central axis
401. The first and second RF feeds 402, 404 may be formed of any suitable
conducting material for coupling RF power to RF coils. Exemplary
conducting materials may include copper, aluminum, alloys thereof, or the
like. The first and second RF feeds 402, 404 may be electrically
insulated by one or more insulating materials, such as air, a
fluoropolymer (such as Teflon®), polyethylene, or the like.

[0033] The first RF feed 402 and the second RF feed 404 are each coupled
to different ones of the first or second RF coils 110, 112. In some
embodiments, the first RF feed 402 may be coupled to the first RF coil
110. The first RF feed 402 may include one or more of a conductive wire,
cable, bar, tube, or other suitable conductive element for coupling RF
power. In some embodiments, the cross section of the first RF feed 402
may be substantially circular. The first RF feed 402 may include a first
end 406 and a second end 407. The second end 407 may be coupled to the
match network 114 (as shown) or to a power divider (as shown in FIG. 1).
For example, as depicted in FIG. 4A, the match network 114 may include a
power divider 430 having two outputs 432, 434. The second end 407 of the
first RF feed 402 may be coupled to one of the two outputs of the match
network 114 (e.g., 432).

[0034] The first end 406 of the first RF feed 402 may be coupled to the
first coil 110. The first end 406 of the first RF feed 402 may be coupled
to the first coil 110 directly, or via some intervening supporting
structure (a base 408 is shown in FIG. 4A). The base 408 may be a
circular or other shape and includes symmetrically arranged coupling
points for coupling the first coil 110 thereto. For example, in FIG. 4A,
two terminals 428 are shown disposed on opposite sides of the base 408
for coupling to two portions of the first RF coil via, for example,
screws 429 (although any suitable coupling may be provided, such as
clamps, welding, or the like).

[0035] In some embodiments, and as discussed further below in relation to
FIGS. 5A-B, the first RF coil 110 (and/or the second RF coil 112) may
comprise a plurality of interlineated and symmetrically arranged stacked
coils (e.g., two or more). For example, the first RF coil 110 may
comprise a plurality of conductors that are wound into a coil, with each
conductor occupying the same cylindrical plane. Each interlineated,
stacked coil may further have a leg 410 extending inwardly therefrom
towards a central axis of the coil. In some embodiments, each leg extends
radially inward from the coil towards the central axis of the coil. Each
leg 410 may be symmetrically arranged about the base 408 and/or the first
RF feed 402 with respect to each other (for example two legs 180 degrees
apart, three legs 120 degrees apart, four legs 90 degrees apart, and the
like). In some embodiments, each leg 410 may be a portion of a respective
RF coil conductor that extends inward to make electrical contact with the
first RF feed 402. In some embodiments, the first RF coil 110 may include
a plurality of conductors each having a leg 410 that extends inwardly
from the coil to couple to the base 408 at respective ones of the
symmetrically arranged coupling points (e.g., terminals 428).

[0036] The second RF feed 404 may be a conductive tube 403 coaxially
disposed about the first RF feed 402. The second RF feed 404 may further
include a first end 412 proximate the first and second RF coils 110, 112
and a second end 414 opposite the first end 412. In some embodiments, the
second RF coil 112 may be coupled to the second RF feed 404 at the first
end 412 via a flange 416, or alternatively, directly to the second RF
feed 404 (not shown). The flange 416 may be circular or other in shape
and is coaxially disposed about the second RF feed 404. The flange 416
may further include symmetrically arranged coupling points to couple the
second RF coil 112 thereto. For example, in FIG. 4A, two terminals 426
are shown disposed on opposite sides of the second RF feed 404 for
coupling to two portions of the second RF coil 112 via, for example,
screws 427 (although any suitable coupling may be provided, such as
described above with respect to terminals 428).

[0037] Like the first coil 110, and also discussed further below in
relation to FIGS. 5A-B, the second RF coil 112 may comprise a plurality
of interlineated and symmetrically arranged stacked coils. Each stacked
coil may have a leg 418 extending therefrom for coupling to the flange
416 at a respective one of the symmetrically arranged coupling points.
Accordingly, each leg 418 may be symmetrically arranged about the flange
216 and/or the second RF feed 404.

[0038] The second end 414 of the second RF feed 404 may be coupled to the
match network 114 (as shown) or to a power divider (as shown in FIG. 1).
For example, as depicted in FIG. 4A, the match network 114 includes a
power divider 430 having two outputs 432, 434. The second end 414 of the
second RF feed 404 may be coupled to one of the two outputs of the match
network 114 (e.g., 434). The second end 414 of the second RF feed 404 may
be coupled to the match network 114 via a conductive element 420 (such as
a conductive strap). In some embodiments, the first and second ends 412,
414 of the second RF feed 404 may be separated by a length 422 sufficient
to limit the effects of any magnetic field asymmetry that may be caused
by the conductive element 420. The required length may depend upon the RF
power intended to be used in the process chamber 104, with more power
supplied requiring a greater length. In some embodiments, the length 422
may be between about 2 to about 8 inches (about 5 to about 20 cm). In
some embodiments, the length is such that a magnetic field formed by
flowing RF current through the first and second RF feeds has
substantially no effect on the symmetry of an electric field formed by
flowing RF current through the first and second coils 110, 112.

[0039] In some embodiments, and as illustrated in FIG. 4B, the conductive
element 420 may be replaced with a disk 424. The disk 424 may be
fabricated from the same kinds of materials as the second RF feed 404 and
may be the same or different material as the second RF feed 404. The disk
424 may be coupled to the second RF feed 404 proximate the second end 414
thereof. The disk 424 may be an integral part of the second RF feed 404
(as shown), or alternatively may be coupled to the second RF feed 404, by
any suitable means that provides a robust electrical connection
therebetween, including but not limited to bolting, welding, press fit of
a lip or extension of the disk about the second RF feed 404, or the like.
The disk 424 may be coaxially disposed about the second RF feed 404. The
disk 424 may be coupled to the match network 114 or to a power divider in
any suitable manner, such as via a conductive strap or the like. The disk
424 advantageously provides an electric shield that lessens or eliminates
any magnetic field asymmetry due to the offset outputs from the match
network 114 (or from the power divider). Accordingly, when a disk 424 is
utilized for coupling RF power, the length 422 of the second RF feed 204
may be shorter than when the conductive element 420 is coupled directly
to the second RF feed 404. In such embodiments, the length 422 may be
between about 1 to about 6 inches (about 2 to about 15 cm).

[0040] FIGS. 5A-B depict a schematic top down view of the inductively
coupled plasma apparatus 102 in accordance with some embodiments of the
present invention. As discussed above, the first and second coils 110,
112 need not be a singular continuous coil, and may each be a plurality
(e.g., two or more) of interlineated and symmetrically arranged stacked
coil elements. Further, the second RF coil 112 may be coaxially disposed
with respect to the first RF coil 112. In some embodiments, the second RF
coil 112 is coaxially disposed about the first RF coil 112 as shown in
FIGS. 5A-B.

[0041] In some embodiments, and illustrated in FIG. 5A, the first coil 110
may include two interlineated and symmetrically arranged stacked first
coil elements 502A, 502B and the second coil 112 includes four
interlineated and symmetrically arranged stacked second coil elements
508A, 508B, 508C, and 508D. The first coil elements 502A, 502B may
further include legs 504A, 504B extending inwardly therefrom and coupled
to the first RF feed 402. The legs 504A, 504B are substantially
equivalent to the legs 410 discussed above. The legs 504A, 504B are
arranged symmetrically about the first RF feed 402 (e.g., they are
opposing each other). Typically, RF current may flow from the first RF
feed 402 through the legs 502A, 502B into the first coil elements 504A,
504B and ultimately to grounding posts 506A, 506B coupled respectively to
the terminal ends of the first coil elements 502A, 502B. To preserve
symmetry, for example, such as electric field symmetry in the first and
second coils 110, 112, the ground posts 506A, 506B may be disposed about
the first RF feed structure 402 in a substantially similar symmetrical
orientation as the legs 502A, 502B. For example, and as illustrated in
FIG. 5A, the grounding posts 506A, 506B are disposed in-line with the
legs 502A, 502B.

[0042] Similar to the first coil elements, the second coil elements 508A,
508B, 508C, and 508D may further include legs 510A, 510B, 510C, and 510D
extending therefrom and coupled to the second RF feed 204. The legs 510A,
510B, 510C, and 510D are substantially equivalent to the legs 418
discussed above. The legs 510A, 510B, 510C, and 510D are arranged
symmetrically about the second RF feed 404. Typically, RF current may
flow from the second RF feed 404 through the legs 510A, 510B, 510C, and
510D into the second coil elements 508A, 508B, 508C, and 508D
respectively and ultimately to grounding posts 512A, 512B, 512C, and 512D
coupled respectively to the terminal ends of the second coil elements
508A, 508B, 508C, and 508D. To preserve symmetry, for example, such as
electric field symmetry in the first and second coils 110, 112, the
ground posts 512A, 512B, 512C, and 512D may be disposed about the first
RF feed structure 402 in a substantially similar symmetrical orientation
as the legs 510A, 510B, 510C, and 510D. For example, and as illustrated
in FIG. 5A, the grounding posts 512A, 512B, 512C, and 512D are disposed
in-line with the legs 510A, 510B, 510C, and 510D, respectively.

[0043] In some embodiments, and as illustrated in FIG. 5A, the
legs/grounding posts of the first coil 110 may oriented at an angle with
respect to the legs/grounding posts of the second coil 112. However, this
is merely exemplary and it is contemplated that any symmetrical
orientation may be utilized, such as the legs/ground posts of the first
coil 110 disposed in-line with the legs/grounding posts of the second
coil 112.

[0044] In some embodiments, and illustrated in FIG. 5B, the first coil 110
may include four interlineated and symmetrically arranged stacked first
coil elements 502A, 502B, 502C, and 502D. Like the first coil elements
502A, 502B, the additional first coil elements 502C, 502D may further
include legs 504C, 504D extending therefrom and coupled to the first RF
feed 402. The legs 504C, 504D are substantially equivalent to the legs
410 discussed above. The legs 504A, 504B, 504C, and 504D are arranged
symmetrically about the first RF feed 402. Like the first coil elements
502A, 502B, the first coil elements 502C, 502D terminate at grounding
posts 506C, 506D disposed in-line with legs 504C, 504D. To preserve
symmetry, for example, such as electric field symmetry in the first and
second coils 110, 112, the ground posts 506A, 506B, 506C, and 506D may be
disposed about the first RF feed structure 402 in a substantially similar
symmetrical orientation as the legs 502A, 502B, 502C, and 502D. For
example, and as illustrated in FIG. 5B, the grounding posts 506A, 506B,
506C, and 506D are disposed in-line with the legs 502A, 502B, 502C, and
502D, respectively. The second coil elements 508A, 508B, 508C, and 508D
and all components (e.g., legs/grounding posts) thereof are the same in
FIG. 5B as in FIG. 5A and described above.

[0045] In some embodiments, and as illustrated in FIG. 5B, the
legs/grounding posts of the first coil 110 are oriented at an angle with
respect to the legs/grounding posts of the second coil 112. However, this
is merely exemplary and it is contemplated that any symmetrical
orientation may be utilized, such as the legs/ground posts of the first
coil 110 disposed in-line with the legs/grounding posts of the second
coil 112.

[0046] Although described above using examples of two or four stacked
elements in each coil, it is contemplated that any number of coil
elements can be utilized with either or both of the first and second
coils 110, 112, such as three, six, or any suitable number and
arrangement that preserves symmetry about the first and second RF feeds
402, 404. For example, three coil elements may be provided in a coil each
rotated 120 degrees with respect to an adjacent coil element.

[0047] The embodiments of the first and second coils 110, 112 depicted in
FIGS. 5A-B can be utilized with any of the embodiments for altering the
phase between the first and second coils as described above. For example,
each of the first coil elements 502 can be wound in an opposite direction
to each of the second coil elements 508 such that RF current flowing
through the first coil elements is out of phase with RF current flowing
through the second coil elements. Alternatively, when a phase shifter is
used, the first and second coil elements 502, 508 can be wound in the
same direction or in an opposite direction.

[0048] Returning to FIG. 1, optionally, one or more electrodes (not shown)
may be electrically coupled to one of the first or second coils 110, 112,
such as the first coil 110. The one or more electrodes may be two
electrodes disposed between the first coil 110 and the second coil 112
and proximate the dielectric lid 120. Each electrode may be electrically
coupled to either the first coil 110 or the second coil 112, and RF power
may be provided to the one or more electrodes via the RF power supply 108
via the inductive coil to which they are coupled (e.g., the first coil
110 or the second coil 112).

[0049] In some embodiments, the one or more electrodes may be movably
coupled to one of the one or more inductive coils to facilitate the
relative positioning of the one or more electrodes with respect to the
dielectric lid 120 and/or with respect to each other. For example, one or
more positioning mechanisms may be coupled to one or more of the
electrodes to control the position thereof. The positioning mechanisms
may be any suitable device, manual or automated, that can facilitate the
positioning of the one or more electrodes as desired, such as devices
including lead screws, linear bearings, stepper motors, wedges, or the
like. The electrical connectors coupling the one or more electrodes to a
particular inductive coil may be flexible to facilitate such relative
movement. For example, in some embodiments, the electrical connector may
include one or more flexible mechanisms, such as a braided wire or other
conductor. A more detailed description of the electrodes and their
utilization in plasma processing apparatus can be found in U.S. patent
application Ser. No. 12/182,342, filed Jul. 30, 2008, titled "Field
Enhanced Inductively Coupled Plasma (FE-ICP) Reactor," which is herein
incorporated by reference in its entirety.

[0050] A heater element 121 may be disposed atop the dielectric lid 120 to
facilitate heating the interior of the process chamber 104. The heater
element 121 may be disposed between the dielectric lid 120 and the first
and second coils 110, 112. In some embodiments. the heater element 121
may include a resistive heating element and may be coupled to a power
supply 123, such as an AC power supply, configured to provide sufficient
energy to control the temperature of the heater element 121 to be between
about 50 to about 100 degrees Celsius. In some embodiments, the heater
element 121 may be an open break heater. In some embodiments, the heater
element 121 may comprise a no break heater, such as an annular element,
thereby facilitating uniform plasma formation within the process chamber
104.

[0051] During operation, a substrate 114 (such as a semiconductor wafer or
other substrate suitable for plasma processing) may be placed on the
pedestal 116 and process gases may be supplied from a gas panel 138
through entry ports 126 to form a gaseous mixture 150 within the process
chamber 104. The gaseous mixture 150 may be ignited into a plasma 155 in
the process chamber 104 by applying power from the plasma source 108 to
the first and second coils 110, 112 and optionally, the one or more
electrodes (not shown). In some embodiments, power from the bias source
122 may be also provided to the pedestal 116. The pressure within the
interior of the chamber 104 may be controlled using a throttle valve 127
and a vacuum pump 136. The temperature of the chamber wall 130 may be
controlled using liquid-containing conduits (not shown) that run through
the wall 130.

[0052] The temperature of the wafer 114 may be controlled by stabilizing a
temperature of the support pedestal 116. In one embodiment, helium gas
from a gas source 148 may be provided via a gas conduit 149 to channels
defined between the backside of the wafer 114 and grooves (not shown)
disposed in the pedestal surface. The helium gas is used to facilitate
heat transfer between the pedestal 116 and the wafer 114. During
processing, the pedestal 116 may be heated by a resistive heater (not
shown) within the pedestal to a steady state temperature and the helium
gas may facilitate uniform heating of the wafer 114. Using such thermal
control, the wafer 114 may illustratively be maintained at a temperature
of between 0 and 500 degrees Celsius.

[0053] The controller 140 comprises a central processing unit (CPU) 144, a
memory 142, and support circuits 146 for the CPU 144 and facilitates
control of the components of the reactor 100 and, as such, of methods of
forming a plasma, such as discussed herein. The controller 140 may be one
of any form of general-purpose computer processor that can be used in an
industrial setting for controlling various chambers and sub-processors.
The memory, or computer-readable medium, 142 of the CPU 144 may be one or
more of readily available memory such as random access memory (RAM), read
only memory (ROM), floppy disk, hard disk, or any other form of digital
storage, local or remote. The support circuits 446 are coupled to the CPU
144 for supporting the processor in a conventional manner. These circuits
include cache, power supplies, clock circuits, input/output circuitry and
subsystems, and the like. The inventive method may be stored in the
memory 142 as software routine that may be executed or invoked to control
the operation of the reactor 100 in the manner described above. The
software routine may also be stored and/or executed by a second CPU (not
shown) that is remotely located from the hardware being controlled by the
CPU 144.

[0054] FIG. 6 depicts a flow chart of a method for forming a plasma in
accordance with some embodiments of the present invention. The method 600
is described below in accordance with embodiments of the invention
illustrated in FIGS. 1-3, however, the method 600 can be applied with any
embodiments of the invention described herein.

[0055] The method 600 begins at 602 by providing an RF signal through a
first RF coil, such as the first RF coil 110 (although the "first RF
coil" of the method 600 may be either of the RF coils discussed above).
The RF signal may be provided at any suitable frequency desired for a
particular application. Exemplary frequencies include but are not limited
to, a frequency of between about 100 kHz to about 60 MHz. The RF signal
may be provided at any suitable power, such as up to about 5000 Watts.

[0056] At 604, the RF signal is provided through a second RF coil, e.g.,
the second RF coil 112, coaxially disposed with respect to the first RF
coil such that the RF signal flows through the second coil out of phase
with respect to the flow of the RF signal through the first coil. Any of
the above embodiments may be utilized to control the phase of the RF
current flowing through the first and second coils. For example, as
discussed above, to create an out of phase condition between the first
and second coils, the first and second coils can be wound in opposite
directions, e.g., the first and second directions 202, 204 as illustrated
in FIG. 2. Alternatively or in combination, a phase shifter, such as
phase shifter 302, or blocking capacitors 302, 304, can be utilized to
shift the phase of the RF current flowing through the first and/or second
RF coils such that the RF current flowing through the first RF coil is
out of phase with the RF current flowing through the second RF coil. In
some embodiments, the phase shifter or blocking capacitor may shift the
phase such that the RF current flowing through the first RF coil is about
180 degrees out of phase with the RF current flowing through the second
RF coil. However, the RF current need not be about 180 degrees out of
phase, and in some embodiments, the phase may be between about 0 to about
+/-180 degrees out of phase.

[0057] At 606, a plasma, such as the plasma 155, may be formed by coupling
the RF signal provided by the first and second RF coils to a process gas,
such as the gaseous mixture 150, disposed in a process chamber. The
process gas may include any suitable process gas for forming a plasma. In
some embodiments, the RF signal may be provided at an equal power setting
to each of the first and second RF coils. In some embodiments, the RF
signal may be provided at a fixed or an adjustable power ratio of between
about 1:0 to about 0:1 between the first and second RF coils. The plasma
may be maintained for a desired period of time using the same or
different settings of the RF current ratio and/or the phase difference of
the RF current flowing through the first and second RF coils.

[0058] Thus, methods and apparatus for plasma processing are provided
herein. The inventive methods and plasma processing apparatus
advantageous reduces additive electric field properties between adjacent
plasma coils in multi-coil plasma apparatus. Accordingly, a plasma formed
utilizing the inventive plasma apparatus has an improved electric field
distribution, and can be utilized to produce a smoother etch surface.

[0059] While the foregoing is directed to embodiments of the present
invention, other and further embodiments of the invention may be devised
without departing from the basic scope thereof.